A known apparatus for determining a seat occupancy is disclosed in JP2009-46093A, for example. According to the apparatus disclosed in JP2009-46093A, load sensors are arranged between a cushion portion of a passenger seat (i.e., a seat cushion) for a vehicle and a floor of the vehicle. Then, the seat occupancy of the seat is detected and determined on the basis of a sum of loads detected by the respective load sensors. Specifically, side leg portions are provided at four corners of a lower portion of the cushion portion of the seat and by means of which the cushion portion is movably in engagement with seat rails. The load sensors are provided at the respective side leg portions so as to detect loads applied to the respective side leg portions. A seat occupancy determination portion compares the sum of the loads detected by the respective load sensors with a predetermined threshold value so as to determine the seat occupancy of the seat.
The seat occupancy state detected by the apparatus is used for controlling an air bag operation. That is, in a case where it is determined that an adult passenger is seated on the passenger seat, the air bag is able to be fully deployed. In a case where it is determined that no occupant is seated on the passenger seat or a child in a child seat is seated on the passenger seat, the air bag is prohibited from being deployed.
However, the determination of the seat occupancy that is simply based on the sum of the loads applied to the seat may cause a trouble. For example, assuming it is once determined that the child seat is attached to the seat and thereafter the vehicle is accelerated forward, the child seat is pressed against the seat to thereby apply a temporary large load to the seat cushion. In such case, because of the temporary large load applied to the seat, it may be mistakenly determined that the seat occupancy state is shifted from a child seat placed state to an adult seated state.
In addition, in a case where the adult is seated on a forward portion of the seat without leaning his/her back on a seat back of the seat, a sufficient load is prevented from being applied to the seat cushion. In such case, regardless of the fact that the adult is seated on the seat, it may be mistakenly determined that the child seat is placed and fastened on the seat. Accordingly, it is difficult to distinguish between the child seat placed state and the adult seated state when determining the seat occupancy of the seat.
Specifically, the aforementioned issue becomes significant when the number of load sensors provided at the seat for the vehicle is reduced for the purpose of cost reduction of the seat. That is, in a case where the great number of load sensors is attached to various portions of the seat, the seat occupancy state may be precisely detected and determined on the basis of variations of detected loads by the various load sensors. As a result, the seat occupancy of the seat is precisely detected and determined.
On the other hand, when only one load sensor is provided at a left side of the seat while only one load sensor is provided at a right side of the seat, for example, the detection of movement or change of the load in a longitudinal direction of the seat cushion is functionally difficult, which results in difficulties in identifying the aforementioned seat occupancy state. That is, the determination of the seat occupancy of the seat is incompatible with a reduced cost of the seat.
A need thus exists for a method and an apparatus for determining a seat occupancy which is not susceptible to the drawback mentioned above.